In recent years, movies featuring 3D video images have gained popularity. This causes people to become familiar with household playback devices that can play back 3D video content from recording media such as optical discs. Household recording devices that can record 3D television programs on recording media and household video cameras that can record 3D video images have also been developed. It is preferable that, on recording media handled by such devices, 3D video content can be recorded in such a way to be also played back as 2D video content. More specifically, it is preferable that the 3D video content recorded on the recording media allows 2D playback devices to play back 2D video images and 3D playback devices to play back 3D video images. Here, “2D playback devices” refer to conventional playback devices that can only play back monoscopic video images, i.e., 2D video images, whereas “3D playback devices” refer to playback devices that can play back 3D video images. It is assumed in this description that a 3D playback device can also play back conventional 2D video images.
FIG. 57 is a schematic diagram illustrating the technology for ensuring the compatibility of an optical disc storing 3D video content with 2D playback devices (see, for example, Patent Document 1). Two types of video streams are stored in an optical disc PDS: One is a 2D/left-view video stream, and the other is a right-view video stream. The “2D/left-view video stream” is used for 3D video playback to represent 2D video images to be shown to the left eye of a viewer, i.e., “left views,” and is used for 2D video playback to constitute 2D video images themselves. The “right-view video stream” is used for 3D video playback to represent 2D video images to be shown to the right eye of the viewer, i.e., “right views.” The left- and right-view video streams have the same frame rate but different presentation times shifted from each other by half a frame period. For example, when the frame rate of the 2D/left- and right-view video streams is 24 frames per second, the frames of the video streams are alternately displayed every 1/48 seconds.
As shown in FIG. 57, the left- and right-view video streams are divided into a plurality of extents EX1A-C and EX2A-C, respectively, on the optical disc PDS. An “extent” is the smallest unit of data that can be read from the optical disc drive (see “Supplement” for details). Each extent contains at least one group of pictures (GOP). Hereinafter, the extents belonging to the 2D/left-view video stream are referred to as “2D/left-view extents,” and the extents belonging to the right-view video stream are referred to as “right-view extents.” The 2D/left-view extents EX1A-C and the right-view extents EX2A-C are alternately arranged on a track TRC of the optical disc PDS. Such an arrangement of extents is referred to as an “interleaved arrangement.” A group of extents recorded in an interleaved arrangement on a recording medium is used both in 3D video playback and 2D video image playback, as described below.
From the optical disc PDS, a 2D playback device PL2 causes an optical disc drive DD2 to read only the 2D/left-view extents EX1A-C in order, skipping right-view extents EX2A-C. Furthermore, an image decoder VDC sequentially decodes the extents read by the optical disc drive DD2 into video frames VFL. In this way, a display device DS2 only displays left views, and viewers can watch normal 2D video images.
A 3D playback device PL3 causes an optical disc drive DD3 to alternately read 2D/left- and right-view extents from the optical disc PDS. When expressed as codes, the extents are read in the order of EX1A, EX2A, EX1B, EX2B, EX1C, and EX2C. Furthermore, from among the read extents, those belonging to the 2D/left- and right-view video streams are supplied to a left-video decoder VDL and a right-video decoder VDR, respectively. The video decoders VDL and VDR alternately decode the video streams into video frames VFL and VFR. As a result, left and right views are alternately displayed on a display device DS3. In synchronization with the switching of the views by the display device DS3, shutter glasses SHG cause its left and right lenses to become opaque alternately. Therefore, the left views are shown only to the viewer's left eye, and the right views are only to the viewer's right eye. At this point, the viewer perceives differences in shape between the left and right views as binocular parallax, and thus sees the pair of 2D video images displayed by the display device DS3 as one 3D video image.
The above-described interleaved arrangement of extents is used when 3D video content is stored on any recording medium, not only on an optical disc. This allows the recording medium to be used both for 2D and 3D video playbacks.